


The Underwater Heart

by paperiuni



Category: Shadowhunters (TV)
Genre: Adventure, Alternate Universe - Fairy Tale, Canon-Typical Violence, Gen, M/M, Merpeople, Princes & Princesses, Romance, Soulmates, With A Twist
Language: English
Status: In-Progress
Published: 2020-10-05
Updated: 2020-12-06
Packaged: 2021-03-08 04:19:48
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 3
Words: 7,756
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/26845759
Author URL: https://archiveofourown.org/users/paperiuni/pseuds/paperiuni
Summary: Two kingdoms, above and under the sea, are in peril. Two young princes bound together by fate must embark on a dangerous journey to save both their realms. The only problem? Neither of them wants to be here.(A fairytale AU with a twisty soulmate thing and bedtime story-sized chapters.)
Relationships: Magnus Bane/Alec Lightwood
Comments: 95
Kudos: 86





	1. Chapter 1

**Author's Note:**

> Hello, darling readers!
> 
> Yes, I'm here with a new fic and the bright new idea to write in a fairytale style and post short chapters that hopefully won't take weeks to write. It's autumn, the season of gentle mysteries, and I need a breather in between the heavier plot stuff of my other WIPs.
> 
> Consider this first chapter a taste of things to come.
> 
> If you want to find me on social media, I am on:
> 
> tumblr @[poemsfromthealley](https://poemsfromthealley.tumblr.com/)  
> twitter @[juneofthepen](https://twitter.com/juneofthepen) and my fic hashtag is #junefic

*

Far across the ocean, in a kingdom whose name is lost to time, there lived a young prince.

The kingdom was small and stubborn, carved out of the wild shore. It was not the mightiest or the most famed, but the people who had settled there, between the wooded mountains and the stormy sea, loved the land. They tilled and husbanded it with care. They built their gates and towers to keep away the greedy neighbour, but opened their homes to the curious visitor. They said their prayers to the old powers and shut their doors when the omen wind rattled the windows and made the fires burn in unearthly colours.

This was a time when the earth and sea did not yet sleep. Dragons roosted in the mountain heights and nameless things swam in the deeps. One could still find a gardener who heard the whispers of her orchard or a woods guide who would never lose the path he set himself on.

From her throne on the shore of the sea, a queen ruled this land with a stern and even hand. She had four children, but in only one, her eldest son, could she see a future ruler.

Prince Alexander was fair in the way of a winter night: black of hair and pale of countenance, tall and strong as a young pine tree, his eyes the colours of the woods at dusk. His mother the queen had taught him both honour and cunning, and the castle master-at-arms honed his skill with the long knife and the hunting bow. They were not the kingliest of weapons, but in the forest and the mountain trails, the heavy mail and gleaming swords of the inland knights only slowed one's step. 

At every Solstice Fair, held twice a year, as the castle gates were thrown open for the people to visit, whispers passed among the gathered folk, from the meanest milkmaid to the lords and wardens of the kingdom. The crown prince was twenty and still unbetrothed. His middle siblings, a blood sister and a foster brother, were already embroiled in their own games of courtship. On the topic of the one marriage that mattered, no one could speak a solid word.

In every other respect, Alexander was made for the throne. Gallant and steadfast, even his reserved nature more a pleasant mystery than a forbidding chill, he was well loved and well respected. He turned an ear to every petitioner, solved their concerns and unruffled their feathers. He was a fearless warrior, but he would always first be a speaker for peace. The lack of a princess or high-born daughter on his arm could slide a little longer.

Over the winter, Queen Maryse's hair went from charcoal to ash. The hunters of the neighbouring kingdom encroached on the foothills. Three returning merchant ships, laden with coin and trade goods, were lost to storms, and sickness scythed through the coastal villages. Princess Isabelle took a guard and her tonics and tinctures to the stricken homes, offering what ease she could. When she returned, she was pale as sea froth, her face beaded with fever. Cloistering herself, she lay in her bed through the midwinter, battling the damp in her lungs.

The queen's advisers voiced their concerns. The queen had three children of her blood. The princess's ill health was an ill sign. If the Lady of the Scales scooped her from this life, it was all the more crucial to see the royal line continued.

It would be best for the fortunes of both queen and realm if her chosen heir could at least select a bride by Summer's Day. It would hearten the common people. It would soothe the fears of the border wardens whose woodsmen had been found dead, drowned in rimy ponds or with their throats cut with glass blades. The omen wind blew more often along the shore.

It was on one such day on the edge of spring that Queen Maryse took the matter to her son. By all accounts, it was not a long conversation. They had it in hushed tones in the castle library.

Afterwards, Alec went out the seaward gate with his hood up, into the wind that spoke with the voices of the dead and the unborn. The sea rolled whitecaps against the rocks where he had scrambled and explored with his siblings in childhood, and later wandered alone when he needed solitude. The sky blustered with black-bellied clouds. The sense of calm the sea always gave him would not come.

His mother had been more patient with him than he deserved. Ever since his father's untimely death, she had redoubled her efforts to mould Alec into the king the kingdom would need. He knew his parents' union had been loveless, a marriage of lands rather than a meeting of hearts. Still, even as a dowager, the queen devoted herself to her people. There was a happiness in duty, she often told him, and she saw in him the same dutiful love that carried her forward.

One day he'd have to wed. Under the old laws, it would never be to a person of his choosing. The best he could hope for would be someone kind-hearted, someone who would stand beside him as a friend as well as a spouse.

Alec walked on and on along the shore, until his boots were wet and his feet ached. The clouds roiled blue and green, the strange driftwood shades of the fires under the sea. He stared at the sea and let the wind scour him. The waves grew, and their tops flickered with luminous streaks as the people of the king in the deep lit their stormlights. Any wise man would have sought shelter, any hollow to hide him. Any other day Alec would have turned back.

That day, a greater force than all the cautions of his teachers drove him on. 

He took one step too many. The slippery shore turned traitor under his boot, and he slid down into the waves. Spring had not warmed the waters yet, and the harsh spirits of the omen wind spurred them on. They dashed the prince mercilessly against the rocks.

It was morning when Alec woke.

He lay waterlogged and shivering among the tidewrack. The sea was smooth as a mirror, dark and silvery in the twilight. His back was sore under his shoulder blade, and as he sat up, a soft echo like a heartbeat started in his ears, resonating in near perfect time with his own.

There was someone crouched over him. Alec, trained from childhood to defend his person, went for the knife in his boot only to find himself bootless and knifeless, and then his gaze met the other young man's.

His skin was a warm brown like aged birch wood, and his eyes flashed a deep, furious amber from under brows that were speckled with pearly scales. Water had sculpted his raven hair to his skull. He sat lithely on his haunches, his breeches and vest too thin for the misty morning. Alec stared at his fine, captivating features and fought the overwhelming feeling that he knew this face as well as his own reflection.

He tried to say as much, through a throat raw with brine.

The young man answered in a voice like a warbling stream, rushing with the same anger that shone in his eyes. His tempestuous gesture revealed a supple membrane between his fingers. The beat in Alec's skull grew louder. He had been saved by a merling, one of the deep folk, who rose on stormy nights to pull the hapless victims of shipwrecks into watery graves.

"Thank you," he said, and got another spout of melodious nonsense in return. "I don't understand."

The merling tilted his head. The beat softened. Hair-thin rings of spun gold shone on his fingers as he warily touched Alec's face, the flesh cool even against Alec's chilled cheek.

"Alexander." Alec touched his chest. "That's me. Alec. Do you have a name?"

The merling pressed his lips, soft and human, together to make a sound, when an arrow scraped across his shoulder. Bright red blood burst from his silver-spattered skin. Alec screamed as he did, as if in the throes of the same pain. 

Six castle guards poured in across the shore in their hobnailed boots. The first of them wrested the young man away from Alec, seeing only the stranger leaned over her half-conscious prince. The beat in Alec's ears rose into a glass-splitting note that seemed to ring round the bowl of the sea itself. He groped towards his rescuer like he was the only point of light in the world.

"Don't hurt him," Alec rasped, and that was the last thing he said before he sank into the dark again.

*


	2. Chapter 2

**Notes for the Chapter:**

> Soooo, this shortish chapter is twice the size of the first one, but that's still reasonable. Right?

*

For the next few days, the crown prince lay in troubled slumber on his bed of lambswool and goose down, and in a cell hewn into the sea cliffs, the captive merling dreamed the same dreams. When Alec woke, he found his heart still beating in a double rhythm, like two palms on the same drum. When he complained, the queen's physician was summoned. The old doctor could only hear the sound of the prince's fine young heart. He was recovering well from his plunge into the spring sea.

Soon enough, Alec had to rise from his convalescence, gird his tunic and put on his new boots. His mother welcomed him with a kiss on the cheek and a stack of foreboding letters. There were signets from all corners of the kingdom pressed onto them. A few bold souls had even sent tiny paintings of their eligible kinswomen, delicate as dolls, at least when captured on canvas.

"You will meet them on Summer's Day," Queen Maryse said, in a tone that brooked no argument. "And you will choose one. Lord Branwell's daughter is a clever one, and actually looks like her portrait."

Alec left her among the letters. The bruise on his back ached like an elf-shot.

His feet carried him through the familiar bustle of the castle grounds, in circles and in loops, until he found himself at the pitch-stained doors that led to the queen's dungeons. The guard let him through with a sidelong look. He was the royal heir; at his word, almost any door in the castle would open. He took a lantern down the winding stairs that smelled of wet rock and seagrass, and worse things besides.

The window in the cell could barely be called such. It was a slanted hole high in the wall that a cat could not have squeezed through. There was at least a straw pallet, a wooden cup and a jug of water. The merling sat curled into himself in the corner, his shoulder dressed with blood-stippled linen.

"Alexander," he said, slow and venomous.

Alec knelt on the dirty floor outside the iron bars and brought out the salves he had begged from Isabelle, and the clean bandages. His hand just fit through the bars. "I want to help you."

The merling sprang from the corner, sleek as an otter in water, and spat in his face.

"The Lady's grace." Alec sighed, and wiped his cheek with his sleeve cuff. "I won't hurt you. I'm sorry our soldiers did."

The merling glared at him. It was still a sight less disheartening than that of his mother with the pile of letters that would seal his fate.

"Can we try that again?" Alec put a hand to his heart, then against the bars. "Alexander. And you?"

His heart thundered, like it wasn't only his own tension spurring it to race. The merling brought his own hand up. Someone had stripped off his spun-gold rings.

"Alexander." The _x_ hummed into a soft _hhh_ sound. Then, after a tiny pause, the merling finished the word he'd begun on the beach. "Magnus."

His fingertips landed on Alec's palm, and it was like Alec was a bell, aching to be struck, the touch reverberating in his every bone. His heart calmed. His breath eased. Looking up, he could tell his companion had also lost some of his fear. They beheld each other across the bars.

Unwinding a linen bandage, Alec mimed wrapping it around his own arm. "I want to clean your wound. Do you understand? Do you have medicine under the sea?"

He imagined Isabelle trying to keep her herbs dry and her salves fresh in the briny realm of the deep king, and a laugh escaped him.

Magnus crouched down, his fey eyes narrowed. A small, nearly silent chuckle rippled from his chest.

Alec could not explain the relief that flooded him. Somehow it was unimaginably right that this battered stranger his mother had imprisoned should be happy.

With the key he had got from the guard, he unlocked the cell door. Magnus shrank back as he stepped inside. It was the act of a trusting fool to enter a prisoner's cell alone, but Alec was moved by a deeper urgency than his own safety.

There was a voice in him that said, against all sense, _He will not harm you._ He knew this as well as he knew the reverse: he would not raise a hand against Magnus, either. He had crept into the dungeons in secret to do the very opposite.

The water in the jug seemed fresh. Alec gestured for Magnus to untie the bandage, which the merling did, in gingerly motions. The arrow wound was not deep, but it had gone a dull red at the edges. Whoever had cleaned it had done a shoddy job.

When Alec made to pour water onto the wound, Magnus grabbed the jug from his hand with a swift, shocked pull, spouting frantic words. He was shaking his head, his eyes gone huge.

Alec frowned. "You don't want me to use the water?"

Magnus held out his own bare forearm. He pressed a finger into the skin, so hard it left behind a bloodless dot. The tiny scales that covered parts of his skin in faint, swirly patterns looked dry and bristling.

"Water," he said, in a near-perfect mirror of Alec's tone. " _Water._ "

"Oh." Alec's heart sank with understanding. A human drowned for want of air. The folk of the deep, then, would shrivel for want of water.

He took his handkerchief and dipped it. Then he put the jug precisely where it had sat, safe by the wall. He cupped a hand under Magnus's arm, warm and solid in his grip, and wiped the wound as gently as he could.

While he worked, Magnus watched him, unblinking. He daubed the gash with a mild salve and bound it up again.

"I have to go," Alec said, half an apology. "I'll make sure you have enough water."

As they pulled apart from their huddle, he felt like a loosely hanging thread had tightened between them. Magnus's face turned wary. "Go," he said, then a string of words Alec could not follow. "Again?"

"I will come again." Alec tucked his wrung handkerchief through the handle of the jug. "I promise."

He got no chance to speak with his mother again that day. Petitioners filled the hall where the queen received them, and the long line of them wound across the bailey like a many-coloured serpent as Alec watched them from his rooms below the western tower.

While he'd lain sick, his own duties had heaped up. He found no comfort in them. His siblings had their own business to attend to, and he was hardly ready to unburden himself. Something had gone horribly awry that day on the beach.

All his life, Alec had known his destiny. He would be sovereign after his mother. He would care for his people, keep the old laws, make fast the borders. Now the ground burned under his heels and disquiet stirred in his breast.

He tossed and turned all night. This prepared him poorly for facing his mother as they met in the breakfast room.

"The prisoner," Alec said, as soon as their plates were empty and business could be brought up. "He's one of the deep folk."

"What of him?" Queen Maryse arranged her silken skirts. "I do not see an envoy from the King in the Deep, come to explain him. In the absence of such, the fact remains that he laid a hand on the crown prince."

Alec blustered. "He didn't _hurt_ me. I tripped over my own feet and fell into the sea."

"Your foolishness is another matter. I have the word of six oathsworn guards that they found him holding you down. Harm to a royal person is a whipping offence, at the very least."

Alec, versed in the laws of the kingdom, knew this quite well. A speechless horror rose in him, as if his mother had proposed to tie him to the whipping post instead.

"You can't," he said before he could think again. "He isn't well. He must—you must—"

Not even her beloved son told Queen Maryse what to do. Her strict visage hardened to ice.

" _Enough_ , Prince Alexander." She cut him off with a sweep of her hand. "I've made my wishes clear. Don't force me to make them into an order. You will marry this year. This is for your sister and your brothers, and the safety of all your people. I'll decide how to punish the prisoner in due course. Put him out of your mind, and put your mind to more important matters. You're not a child anymore."

It was seldom that she scolded him. Being a rare occasion, it struck him with twice the force it would have for his more rambunctious siblings. Shamefaced, Alec sketched a bow and retreated with a mumbled, "Yes, Your Grace."

The conversation kept stinging him like a splinter under his nail as he was again swept up in affairs high and low.

Spring was a hectic season. Summer's Day was still two moons away, but the preparations were starting. Planting was in full swing. The queen appointed her foster son, Jace, as captain of the castle guard. As the first step of a promising courtship, Princess Isabelle met the son of a lord from the southern vales and then declared him an insufferable buffoon in the middle of a royal dinner. Hilts were rattled, bitter accusations were thrown. Alec spent the rest of the night convincing the young master that his sister had not meant it, narrowly averting a political incident.

In private, Alec told Isabelle that she'd been dead right about the buffoonery. The prospective match, however, was in shambles.

Among all this, it took Alec three days to steal down into the dungeons again. Every waking hour, he fought the soft call of the second heartbeat that he had, inevitably, begun to think of as belonging to Magnus.

The pain under his shoulder blade had faded. Still, when he was alone, he found himself groping for the spot. He could see no mark or injury there, but the skin remained tender.

If the whole castle was busy, his mother the queen was even more so. For the first time in his life, Alec took advantage of her preoccupation. He made a few discreet requests to the servants, who liked him well, and thus honoured his discretion.

He entered the dungeons on soft feet as the stars were coming out. Magnus was in his cell, a coiled, silvery shadow on the wall. His fingers and toes were curled into cracks between the stones so he could press his face to the narrow slit of a window. Alec had no doubt that if the gap had admitted him, he'd have already made his escape.

"Looking for the moon?" he asked.

Magnus dropped back to the floor and swung around. Climbing the wall apparently did not bother his still-wrapped shoulder. His voice was hoarse. "You come again."

"I said I would." Alec wanted to shift his weight. "I'm sorry I took so long."

The pallet now sported a blanket and a pillow, and two water buckets, one empty, one full, stood beside the door. Alec flushed with abrupt shame. He'd given an order and it had been followed to the unadorned letter, no more.

"I don't think." Magnus's words fit together oddly, as if he wanted them to slide and mesh into one another, but they were clear. "Not sorry, you. Your guards keep me. Watch me."

"You're talking a lot more," Alec said. He couldn't make sense of his desire to be here. It was not a _want_ as such, not something that brought him joy. It both compelled and centred him.

"Your guards talk. People, too." Magnus gestured at the grimy corridor. "I listen. Not much to do."

With a stoic shrug, Alec accepted this for now. He knew nothing of the way merlings picked up languages. "I really _am_ sorry. I want to ask you so many things. I—I wish I could let you out, but my mother..."

"The queen," Magnus said. "I know this."

"Yes." Alec made a face. "Listen. I'm going to go. A guard will come along shortly. Go with her. Then we can talk."

Magnus grit his teeth. In the darkness, the scales on his face seemed to glimmer like his eyes would under lantern light.

"Please?" Alec slid his hand through the bars again, with the same gesture of the upturned palm, like a supplicant to the Lady. Not that Magnus would understand it. The gods of the ocean were different, ancient and unknowable. Their wrath fell in storms and tidal waves, and their favour could not be courted by any mortal.

Magnus set his palm against Alec's. His skin felt papery, drawn taut over the bones. The curves of his nails pressed against Alec's skin, and his teeth flashed as he said, "Be nice. I can do this."

Alec didn't dare to actually grasp his hand. "Thank you."

Then he slipped away, his palm still tingling, and went up to his own rooms. As the heir, he had the highest floor of the western keep to himself. Usually it felt like a pointless luxury, but it was useful for tonight.

He did not have to wait long for the knock. The guard, one of his own, pushed a surprisingly meek Magnus, shackled by the wrists, over the threshold. Alec thanked her with a nod, and shut the door.

It was late, most of the castle long asleep. Candles burned in their holders on the walls. Alec had always preferred simplicity in his rooms, but the firelight made the carved wood and the thick velvet curtains shimmer. Magnus's eyes darted across the paintings, the desk, the shelves full of precious, hand-copied books.

"Very fine," Magnus said, almost cheekily, rounding out the thought with a few melodious words in his own tongue. "Why here?"

There was a corridor past Alec's rooms that led to the western tower. In more turbulent times, the tower had housed political prisoners, those too important to simply cast into the dungeons to await royal justice. For now, Alec gestured for Magnus to follow him in through the front room.

His guard would have taken her post right outside. Thankfully, Magnus moved with nary a clink of his shackles. At the threshold to the bedroom, Alec slid out the pins that held the manacles in place.

"I can't give you the sea," he said, "but... I hope this helps."

Alec had asked for a bath to be drawn for him. The copper tub no longer steamed, but the air had gone a little humid, warmed by the fire in the grate. Magnus looked at the tub, its round, fire-reddened side, and back at Alec again. His face betrayed open wonderment.

Alec drew a breath. "I'm going to sit over there, by the bed. You can take your time."

Whether or not merlings cared for modesty, Alec did, so he leaned into the high back of his reading chair and stared fixedly at the candle on the bedside bench. There was silence behind him. Then, when he was about to peer around out of sheer nerves, cloth swished, a few footfalls sounded, and water splashed softly.

"You can look." Magnus chuckled, rich with some private amusement.

Alec turned so he could see over the back, on his knees on the seat, like a curious child. Magnus was submerged to his chin, one foot angled on the rim of the tub, his hair fanned on the surface of the water. Relief crept over Alec like a warm wave.

He let himself dwell on it for a moment before he said, "Why were you on the shore?"

Magnus sighed a complex kind of sigh. His patchy vocabulary did nothing to erase the wry weight in his reply. "You call me, little prince. I come."

"I _called you_?" Alec clapped a hand over his own mouth. Unseemly noise from his rooms would bring guards beyond the one he could trust, and that would be it for his whole clandestine tête-à-tête. "I fell into the sea!" he said, through his fingers.

"The sea draws you," Magnus said, slowly. His eyes held Alec's like a pinioning arrow. "The land draws me. I come to do what the old laws ask."

This had not been covered by any tome of law Alec had been made to study. As Magnus spoke, each word tugged at him, quiet and inescapable, like they were peeling away a shadow that had lain within him all his life.

"Who are you?" he asked. "You spent a week in a cell, and you're... talking better by the hour."

"I am clever, little prince." Magnus laughed, as if honestly delighted, as Alec's expression soured. "You talk and I learn. Every word."

"I can tell." Alec gathered his dignity. "What laws are those? Who sent you?"

Magnus rose enough to bare his shoulders and the soaked bandage, his chin set at a measured angle. A streak of nobility shone in his posture, a luminous sheen in his gold-flake eyes. "The King in the Deep," he said. "My father."

*


	3. Chapter 3

*

Alec sat in stunned silence while Magnus submerged himself once more and then climbed briskly out of the tub. The sight of gleaming-wet skin was enough to drop Alec back into his seat, his throat flushed hot. His back pressed tight to the padded back of the chair.

Never in recorded history had the kingdom _had_ a delegation from the Undersea. His people treated the seldom-sighted merlings with the kind of fear and caution reserved for the elements. When Queen Maryse had said there was no envoy from the Deep King, she'd meant to reproach Alec for a childish fantasy.

"I don't understand," Alec said. It might soon become a refrain. "You're alone. Wouldn't your father send you with guards and servants?"

To his surprise, Magnus laughed, bitter and humourless. "I _am_ alone. You don't understand. I make a promise to you. You speak to me, every day, and I explain."

"I can't really keep sneaking down to the dungeons. My mother will get suspicious."

"Don't put me in chains again. I can stay here. Room enough for ten of us." It was most likely a joke, but it still pricked deep into Alec's conscience.

"You know I can't! The queen's guards took you prisoner. I'm not king yet, I can't pardon you, even if I wanted to." He flinched at his own words. "I'm sorry. I didn't mean like that. I would want to. Of course."

Magnus's shadow skimmed the edge of Alec's vision as he went back to his discarded clothes, presumably still rather damp. He wrung out his hair onto the floorboards. "You're clever, too. Think it out."

Alec sighed a heartfelt sigh. However, beneath his dismay, wheels were already turning in his mind.

The plan he made was this: his brother was now the newly minted guard captain. Jace still took advice from the retired captain and his senior officers, but with a nudge from Alec, he signed off on a small change of quarters without their mother being none the wiser.

For the last fifty years, the tower above Alec's rooms had only housed swallows, spiders and some enterprising mice. Upon his furtive request, it was swept and scrubbed to as welcoming a guise as possible, given there were still bars on the windows and a rusted lock on the door. Alec took an armful of pillows and furs from his bed to cover the much humbler cot beside the fireplace that warmed the rooms.

Two days later, his guard brought Magnus up again. With a tight, skittish feeling in his chest, Alec led him up the curved staircase and showed him the rooms. They were joined by a doorway, furnished to as great comfort as Alec and a couple of trusted servants had managed. Soft rugs muffled the stone floor. There were two chairs around a table and a large washbasin set in a stout wooden stand. Alec had also taken the liberty of sneaking in a few of his books.

Rubbing his wrists, freed from the manacles, Magnus went to a window. "Now I see the moon."

Alec had not expected thanks, and Magnus's tone was dry, but the dash of approval there washed away his misgivings.

The moon waxed to fullness and began to wane again. In secret, their strange cohabitation continued.

As soon as he could steal away in the evening, Alec turned the iron key in the old lock and joined Magnus for lessons. That was how he quickly came to think of these late hours. He'd sit on a chair or the cot and tell Magnus about his day, or a visitor, or the kingdom itself. When Alec's own stories ran out, he opened a book and read dusty old chronicles or long, winding poems of knights-errant and talking beasts and maidens trapped in towers.

"That is me, then," Magnus said, without venom, when the first fair damsel appeared in a verse. "I hope this girl has more to do in her tower."

"They seem to do a lot of spinning, these captive princesses." Alec had soon learned that Magnus bore an air of firm insouciance about his captive circumstances. Any pity or rue was swiftly rebuffed, but now, Magnus's laughter was bright and almost sweet.

"You get me a spindle, little prince, and we can talk."

Alec smiled back at him, and turned the page.

Their conversations grew more mutual as Magnus soaked in new words, at a pace that would have astonished any scholar. He asked endless questions about the castle, Alec's siblings, his childhood, but offered only a few morsels about himself. He still wouldn't elaborate on his bold claim of royal ancestry, either. "I made you a promise," he'd reply to Alec's unsubtle prodding. "When it is time."

Alec had passed a word to Jace to keep a careful watch on the seaward walls. He listened anxiously to tidings from the fishing hamlets along the shore, but no sign of the Deep King's fury over a stolen son manifested. Even the omen winds and the fierce spring storms seemed to abate, and the year turned towards summer.

Then came the day the mark appeared on Alec's back.

It was his sister who first found it. Alec was helping in the orchard, pruning dead wood from the cider apple trees, and took a bruising tumble when a branch cracked under him. To escape the censure of the royal physician, he sought out Isabelle and her apothecary. She clicked her tongue, too, but went for a salve while he pulled off his shirt.

"Merciful Lady," she whispered. "Alec, what is this?"

Her misty mirror showed three opalescent teardrop shapes under his shoulder blade, fanned out like flower petals. Each was the size of his smallest fingernail and as flawless as if stamped there with the finest inks from the castle chancery. They blended perfectly with the texture of his skin.

He could have lied. Bringing another person into his confidence was a risk. Isabelle had already helped him smuggle medicine to the cell for Magnus's wound. So, holding her hand between his own, Alec told his sister about the day on the shore, the merling, and the echoing heartbeat that still filled his ears, his entire being, when he got too far away from Magnus.

"You can't tell Mother," he said, imploring, to round off his tale. "She's so set on marrying me off. If she catches wind of this, or anything that might foil her plan, she'll have Magnus whipped, or worse. I can't..."

He had no words to fill that sentence. By day, he still acted the royal heir, the strapping prince, the clear-headed arbiter receiving petitioners while Queen Maryse was consumed by greater affairs of state. By night, he kept company with a stranger, a trespasser, a man whose rare delight seemed to matter more to him than his mother's approval.

Isabelle put her hand on his cheek. "We'll work this out. You saved me from a wretched courtship. Whoever this merling is, we can handle him together."

"I have him handled," Alec said, flustered. "I just need to know what to _do_ with him."

Her cheeks dimpled with mischief. "I'd guess you already have an idea, sweet brother."

Alec did. He dithered about it for the afternoon, but there was no other way. No book in the library could help him. The queen's scholars and scribes might have answers for him, but none he could get without alerting his mother to this mystery.

Magnus was at the window again as Alec entered the towertop rooms. The moon, shrunken to a sickle, graced the high horizon. The waves sighed against the cliffs below the castle.

Alec undid his vest, bunched up his shirt, and pointed at the mark. "I'm afraid your time is up. What is this? It has something to do with this—this thing between us."

Sly appreciation flickered on Magnus's face as he glanced Alec over. However, when he saw the mark, a hushed gravity weighed his brows and tightened his mouth. He traced it with a cool fingertip, and a curious little shudder twisted up Alec's spine. His heartbeat thickened. So did Magnus's.

Magnus canted his chin up so he could look squarely at Alec. "We are bound together, you and I. This you already know. Now the scales are set in your flesh. You've embraced me. My mark is on you."

Alec felt his temper flare. "Look, I know I've been reading you a lot of poetry, but I could use some plain words right now!"

"The old laws," Magnus said. "Do you know them, Prince Alexander?"

"Of course I do. Everything since the foundation of the kingdom. They say nothing about any merling marks, or the Undersea, or whatever it is you did to me on the shore."

"Do you blame the leaf for the wind that carries it?" Alec had watched Magnus, even if mostly by candlelight, for weeks. He'd come to know Magnus's slippery smiles and his mobile, lithe posture. He looked like a different person now, statuesque and still.

"Why did you save me?" Alec countered. "What do you want here?"

Magnus did not shirk. "There are compacts older than those in your books. The harmony of mountain, meadow and mere. The union of the tillers and the hunters. Your people's memories have got short, but I know. I know well. I was born of such a union, after all."

Alec sat down, understanding and confusion in a deadlock within him.

"You're..." Alec groped for the word at the tip of his memory. "You're a changeling. A child of land and sea. I thought they were only stories."

"I'm real enough." Magnus's nimble fingers wrapped over his elbows. "I told you no lies. I'm a royal bastard of the Deep King himself. Not fit to wear the crown, but useful when you need a loyal pair of eyes and hands above your watery realm."

"Doesn't sound like you came for a diplomatic visit." Alec tried to smile, if only to lighten Magnus's grave tones.

"I didn't." Magnus took a seat next to Alec. "I came seeking a solution. The deep folk can't walk on land, so the task fell to me. My father says that there is a rot at the heart of our realm. An old, nameless power that stirs in its sleep." He cut a glance at Alec. "Your people must have noticed it, too. Sickness, unrest, corruption of the earth and those who live upon it. These are its tools."

Blinking back his awe, Alec realised he was gripping Magnus's wrist, so hard his hand trembled. He unhooked his fingers with a mumbled apology, then found his voice. "You knew all this and you still stopped to help me? I've held you in this tower for weeks! What about your search?"

"I won't say I was expecting it," Magnus said, with false airiness, "but my search led me to you. There is a bond between us. You feel it, too. It grows by the day."

"Yes. What does it _mean_? Why do you matter so much?" Alec swallowed the _to me_ that would have fit at the end.

"It means that wherever we go, we must go together." Magnus stood to weave a loop across the rug. Alec had offered him shoes to wear on the cold stone, but he remained barefoot. "In the days before your kingdom, before your books of law, the land and the sea would join forces in times of need. Between two people from different worlds, a bond would be born. Their destinies would be linked, as would their lives."

Alec felt like he'd been walloped with a forge hammer. His breath wheezed softly. In comparison, Magnus was so sombre. You might even have said he seemed resigned. To the state of things. To his fate, which was now, evidently, also Alec's own.

"I can't _leave_ ," Alec said inanely. "The Solstice Fair is in a month! My mother expects me to find a _wife._ " That came out too close to a curse. "Can't you just take it back? Find somebody else? Not that it doesn't sound important."

Magnus's sun-glimmer gaze was steady. "I didn't ask for you, either."

For a while, Alec sat twisting his hands together and ruminating. It'd been a hard winter, and no one could say how summer would bloom. He remembered Isabelle, white as death on her bed, fighting for an easy breath. He thought of his brothers, of Jace's newly shouldered duty and Max at his lessons and at play, still clinging to childhood's simple joys.

A tension lingered among his people. Doors were barred that would normally stand open day and night. What trade caravans left for the borders were closely guarded. The priests of the Lady of the Scales frowned over sheep entrails and five-wood bonfires, trying to discern her displeasure.

No matter how captivating, Magnus hardly looked the part of a champion to deliver them. Alec was sure _he_ did not look it.

He braced himself. "What do you need me to do?"

Magnus's face gentled. "My father gave me a piece of counsel. In your kingdom, there is a place called Old Man's Wood. A soothsayer lives there, a wise man who is supposed to know the realm and its needs."

"Oh." That was more practical than Alec had assumed. "That's close, actually, but I've never heard of anybody living there. If we follow the river, we could..." He trailed off with a gasp.

"What is it?"

"I just realized," Alec said, "that all things considered, I'd rather go with you than meet a flock of eligible ladies on Summer's Day."

Magnus smiled one of his sharp, fleeting smiles. "You flatter me, little prince. Is it settled then?"

Right then Alec could only feel one rhythm, one sound in his body. He could not tell the beat of Magnus's heart apart from his own. "Yes. Yes, it is."

Magnus nodded, only once.

It took Alec a long time to fall asleep. Once he did, he dreamed of the lightless depths of the ocean, and of swimming across churning waves, swift as an arrow shot, and, lastly, just before morning, of the brilliant pupil of the moon through water, floating in the heavens.

They'd have to make their escape the following night. It was the new moon, and they could slip away sight unseen. Alec had stretched the goodwill of his own servants nearly to the breaking point. What was more, he did not want them implicated in his disobedience. The disappearance of the crown prince would put the whole town in an uproar.

And his mother the queen was set in her ways, stolid as a hill. She'd have no grace for Alec's abrupt change of heart, nor a sympathetic ear to his concerns about the strange plights that seemed to plague the kingdom. She saw human greed and cruelty behind them, or blind chance, not a sinister power out of old tales.

Alec was not sure he believed that part, himself. Still, he couldn't deny the pull he felt towards the capricious bastard prince of the deep.

He should at least investigate, no?

That said, there was one other person Alec would inevitably get in trouble: his brother, the guard captain. They'd grown up together, one to rule, the other to command, and been inseparable all the way to adulthood. Queen Maryse's wrath would fall on Jace if she even remotely suspected he'd been involved in Alec's flight. For all his good qualities, his brother was bold and brash and almost as terrible at lying as Alec himself.

To get around this hurdle, Alec had to go to his other age-mate sibling. Isabelle, in turn, could slide through the truth like a cat through a crack in the wall. In any case, he'd already told her too much.

At sunset, he excused himself from supper by pretending he was poring over a trade contract his mother had given him to draw up. She nodded, distracted but approving, and bade him goodnight.

He waited three turns of the small hourglass, like Isabelle had told him to. Then he took the packed bag from under his bed, his bow and quiver from the wall rack, and his good hunting cloak from the wardrobe. A clink of keys and whisper at the door brought Magnus to him. When Alec had asked what supplies he'd need, Magnus had merely shrugged. _My freedom_ , he'd said. At least Alec was giving him that.

Alec had a shuttered lantern, but as he bent to light it, Magnus offered his hand. "Your light will show in the dark. You lent me your words. Let me lend you my eyes."

Alec grasped his hand. The dim staircase rose into sharp relief in his vision, as if the air had a very faint blue glow to it. He banked his nervous excitement as they went down the curving staircase, and then out the little door the servants would use when they came in. As a child, Alec had known all the hidden passages and shortcuts of the castles. He was too big and tall now to employ some of them, but the back stairs and side doors were still there.

Now and then they'd hear faint groans behind a door. A guard sat ailing at her post, her helmeted head in her hands, as they slipped past. Alec winced at a more distant sound of somebody being sick. A maid rushed down a staircase with linens and a bucket of water; they huddled into a dark window alcove, Magnus's shoulder tucked against Alec's stomach, their legs in a jumble.

"My sister put something in the stew," Alec whispered, all too aware of how tightly they were squeezed together. "She swears they'll only be sick for the night. It'll look like spoiled ingredients. And less like incompetence on the guards' part."

"She sounds like a most devious woman," Magnus said, too studiedly amused. "And a good accomplice. I have no siblings, at least none that would do a thing like this for me. I'd like to meet yours someday."

Alec almost asked for details, but by then, the corridor below had fallen silent. They hurried ahead under cover of the general distress that gripped the castle.

They came out through the postern gate and, once across the moat, ran pell-mell into the orchard. Magnus moved like a shadow, light on his feet, tugging Alec over stray roots and loose stones that tried to trip him. A wildness seemed to seize them both, a benign spirit of the crisp spring night that could take them anywhere. The smells of dew and turned dirt surrounded them.

At last, Magnus halted. He lifted his head and gave a low, sonorous call.

"What are you doing?" Alarmed, Alec looked around. They weren't too far from the town yet. His bow wouldn't do them much good in the dark. Even then, he would not have shot at his own guards.

The brush beside them rasped. Magnus crouched down with a hum of gentle joy. He spoke in his own language, and a four-legged figure with a shimmer to its pale coat emerged. It was a cat, a large, sleek creature whose ear tufts curled like the trailing ends of summer clouds. In its mouth, it held a smattering of delicate gold rings.

Magnus cupped his hand so the cat could drop its curious burden in his palm.

"Those are yours," Alec said, half guilty, half amazed. He'd forgotten, among all the other skullduggery, to even look for Magnus's missing jewellery.

"So they are. Fane kept them for me." Magnus slipped the rings back onto his fingers. "She's also scouted a route to the river for us."

"And Fane is..." Alec looked at the feline. She looked back, with pitch-dark eyes that seemed speckled with stardust. 

"A tide-cat." Magnus rose. "She can slip in and out of most places. However, I've sorely tried her patience with this detour to your charming tower, so, shall we be off?"

The castle loomed behind them against the shrouded sky, a mass of parapets and flickering torches. Gripping the stave of his unstrung bow, Alec turned away. "I'm right behind you."

*

**Notes for the Chapter:**

> _Fane_ is an archaic word for a temple, and you know, _Church_ didn't really suit this setting. Anyway, every fairytale hero needs a cool animal companion.

**Author's Note:**

> Comments are a delightful thing! Or come yell at me on:
> 
> tumblr @[poemsfromthealley](https://poemsfromthealley.tumblr.com/)  
> twitter @[juneofthepen](https://twitter.com/juneofthepen)


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